Laser printers use a coherent beam of light, hence the term “laser printer,” to expose discrete portions of an image transfer drum thus attracting the printing toner. Toner is a mixture of pigment (most commonly black) and plastic particles. The toner becomes electro-statically attracted to exposed portions of the image transfer drum. The toner is transferred to paper, or other medium, as it passes over the rotating image transfer drum. Subsequently, the paper is heated so that the plastic is melted thereby permanently affixing the ink to the paper.
The vast majority of commercially available desktop laser printers include replaceable or removable toner cartridges that incorporate an image transfer drum, a toner tank, and a metering system. A drive mechanism is connected to the drum and metering system. Modern toner cartridges often include a variety of sensors that interact with the laser printer to indicate the status of the cartridge. Indications relating to toner level, print quality and general cartridge function are often included as well. A large number of types and sizes of toner cartridges are currently available. The sensing system typically includes an encoder wheel interconnected with a rotating agitating paddle within a cylindrical toner tank. Movement of the agitating paddle feeds toner into the metering system. The encoder wheel reports the movement of the agitating paddle wheel through the toner reservoir.
The toner cartridges of the prior art employ sealing mechanisms which leave gaps at the lateral edges of the doctor bar and developer roller through which toner can escape. Therefore, what is needed is a sealing mechanism which seals the developer roller and doctor bar on all sides, preventing the escape of toner.